This invention relates to a ball-equipped screw and nut mechanism for the conversion of rotary motion into motion of translation, and the reverse conversion.
Mechanisms of this type are already known wherein the nut includes an added cylindrical component. This component includes an inside surface in contact with a thread of the screw, and adapted to transfer the balls from one end to the other end of a section of the same helical groove of the nut, passing over the screw thread so as to create a closed circuit for circulation of the balls. This known version of the mechanism however presents certain disadvantages. It is the inside surface, itself, of the added cylindrical component which provides a guide for the balls in their transfer from one end to the other of the helical groove section of the nut, even though, at the time of this transfer, the balls must roll in contact with the screw thread. The outside surface of the screw threads of the mechanisms of this kind is not generally buffed, and may frequently be irregular, particularly when the helical grooves of the screw have been adapted by embossing the metal. Consequently, transfer of the balls from one end to the other of the helical groove section of the nut is accompanied by friction, and potentially by heavy impact shocks, reducing the efficiency of the motion conversion mechanism, and causing it to function in a noisy manner. Moreover, in this known version, the cylindrical component is added to the outside surface of the nut, thereby making it necessary to provide a means to immobilize the cylindrical component in the radial direction. This complicates manufacture of the nut, and makes it more costly.
In another known version of a ball-equipped screw and nut mechanism of the type considered, the nut contains two openings of cylindrical or oblong shape, joined together by a slot adapted in the outer periphery of the nut, and in which two added components are engaged. These added components are adapted to transfer the balls from one end to the other of a single helical groove of the nut by means of a duct whose innermost wall consists of the bottom of said slot. In this version, the transfer of the balls between the ends of one section of a single helical groove of the nut is effected without material contact between said balls and the threads of the screw. However, machining the nut in this known mechanism is complicated and costly, due particularly to the necessity of adapting the shapes of the various openings, as well as to the added components. Moreover, since the axial transfer of the balls takes place near the outer surface of the nut, the latter must have substantial radial thickness, and consequently, substantial weight and bulk.
There is known, finally, a ball-equipped screw and nut mechanism of the type considered, which comprises, for transfer of the balls between the ends of one section of a single helical groove of the nut, an opening in the shape of an S, which is adapted in the lateral wall of said nut. In this opening there is immobilized, for example, by a welded plug, a tabular piece, likewise S-shaped, which serves to guide the balls over the screw thread, without contact with the thread. The manufacture of the nut of this known mechanism is therefore very complicated and costly.
It is thus an object of the invention to provide a novel and unique ball-equipped screw and nut mechanism which is less bulky, less complicated and less costly than prior such mechanisms.